Very rare chance to obtain this recipe when crafting Rank 2 flasks. Note that you don't automatically learn this like other Alchemy discoveries; the recipe will appear in your bags and must be learned, so be vigilant for this!This rank has a chance to proc up to 20 (potentially more) flasks with a single craft!

NOTES:

You must learn the Rank 1 recipe of the flask in order for the Rank 2 recipe to drop.

You must learn the Rank 2 recipe of the flask in order to get a chance for the Rank 3 recipe.

Legion Herbs

Below is a summary of the various herbs, their sources, and notes on collecting them.

Gathering these has a chance to produce no herbs, and instead give you the vendor trash Polvo de rosa luz estelar. Ranking up your Rosa luz estelar gathering skill will increase your chances of a successful gather, with Rank 3 granting a 100% chance.

I believe the Crucible & Burette chains will not be offered until you've done the alchemy quests in between (you'll need to make/buy Skaggldrynk to complete them at minimum) - so all up you're probably looking at:

Five quest chains

Eye of Azshara dungeon

Neltharion's Lair dungeon

Reaching level 110

Convincing a group to do a special boss in Vault of Wardens (some specs, with passable gear, can get away with doing a normal run & then go back and solo the boss)

So this is not a trivial process - if you're just interested in a few flasks for raiding, you're probably better off spending your time farming herbs to sell. On the positive side, it is a more interesting story than "that'll be 9 gold, here's your recipe, enjoy your flasks".

There's a more in-depth writeup in the Alchemy Guide if I haven't dissuaded you ;)